1. Field of the Invention.
The present invention relates generally to pore size measurement and specifically to a method for determining pore diameters by the technique of positronium annihilation.
2. Description of the Prior Art.
Pore volume and pore surface measurements are used in the evaluation of physical properties of various materials. For instance, this information is used by chemists to study catalytic properties of reactants or additives; by geologists to predict the amount of fluids or gases trapped within the pores inside subterranean formations or to evaluate how much water is wasted by soaking into the ground of water reservoirs. Material scientists use pore volume and pore surface measurements to estimate the strength, thermal expansion, conductivity, and other properties of polymers, composites and amorphous materials.
At the present time, only the BET technique has been commonly used to study pore sizes. This technique is expensive, requires long sessions in use and has poor accuracy for pores smaller than about 40 Angstrom in diameter. Typically, the error in this region exceeds 100%. Recently, great efforts have been expended to improve the BET method and to develop an alternative technique. For example, electron microscopy, X-ray scattering and NMR on hydrogen have been used to evaluate pore sizes and pore distribution in different materials, but none has been accepted as a universal tool.
A need exists for a nondestructive testing method for determining pore sizes smaller than about 40 Angstrom in diameter with greater precision.
Another need exists for such a method for determining the pore sizes of naturally occurring pores in the range from 5 to 300 Angstroms in a specimen material which is less expensive than presently available techniques and which requires shorter sessions to run.